1. Field of the Invention
The invention relates to a torque tube connecting a power transmission unit, to which drive force is input via a power transmission shaft forming a portion of a power transmission path of a vehicle, to a non-rotational member.
2. Description of the Related Art
Japanese Patent Application Publication No. 2006-143130 (JP-A-2006-143130) describes a toque tube used in a vehicle in which drive force is input to a power transmission unit via a power transmission shaft forming a portion of the power transmission path of the vehicle. The torque tube covers the outer face of the power transmission shaft and thus connects the power transmission unit to a non-rotational member.
The torque tube receives drive force, brake force, and reactive torque and thereby suppresses the vibration at the drive line of the vehicle (drive shafts, propeller shaft). Further, the use of the torque tube eliminates the need of providing the upper control arms and thus enables lowering the vehicle floor.
One type of such torque tubes may have (a) a flange member having a cylindrical hub portion and an attachment portion protruding radially outward from one end of the hub portion and attached to the power transmission unit; and (b) a tubular member one end of which is fit in the other end of the hub portion and welded along the end face of the one end of the hub portion and the other end of which is secured to the non-rotational member.
Meanwhile, in a state where drive force, brake force, or reactive torque is produced, that is, when the vehicle is accelerated or decelerated, the produced force or torque causes bending movement on the torque tube, and this bending moment acts substantially in the vertical direction of the vehicle. Typically, the tubular portion has a generally circular cross section and the end face of the other end of the hub portion is substantially parallel to a plane perpendicular to the longitudinal direction of the tubular portion, and the hub portion is welded along said end portion, that is, along a generally circular weld line over the entire circumference. Therefore, the stress acting on the torque tube due to the aforementioned bending moment undesirably tends to undesirably concentrate at the welded portions, at which the shape sharply changes, on a plane that extends through and parallel to the drive force transmission shaft vertically with respect to the vehicle.